Mechanical-metallurgic process for repairing machines or machine components damaged by cracks, fissures, wearings or squashes made of metallic material difficult to weld and of any forms

ABSTRACT

The present invention relates to an integrated restoration process in which material parts are repaired to provide a renewal part which is stress free. The invention includes cleaning, analyzing and sampling the surface of the element to be repaired and selecting the proper additional material.

BACKGROUND OF THE INVENTION

This invention refers to an integrated process for repairing by weldingof machines or machine components made of metallic material of anychemical compositions and difficult to be welded, damaged by cracks orfissures because of fatigue or overload and squash or excessive wearusing the correct combination of machanic, thermic and metallurgicactions, in order to eliminate or minimize internal stresses accumulatedduring the machine or component operational life, remove and repair thefailure-crack, fissure, or squash--and guarantee a minimum residualstresses after repair, being the machine or component in an originaltechnical condition, as far as strength and mechanical-metallurgicintegrity are concerned.

Until this invention, the loss was complete in respect to the failuredue to squash or excessive wearing in machines or components, made ofmetallic material difficult to be welded, because of high sensitivity tothermo-mechanic stresses and easy transformation into more energeticmetallurgic phases susceptibility to the formation of cracks-inducted ina process of localized heating, when such elements are, also acharacterized by complex forms and favourable to additional loads suchas of the type of mechanic restriction or high variation in sectionmodules. The whole machine or component had to be replaced. In such asituation, besides this total loss, the long and expensive time themachine remains stopped for repairs must be computed.

Up to now, the repair of elements which had problems in simple or morecomplex constructive situations covered by this patent followed themethod of welding preceeded by pre-heating, based on the control of thetemperature of the base metal, and a heat treatment for stress reliefafter the weld. In such conditions, the well-known procedures of heatweld have been adopted, in ovens as well as in determined sections orelements by means of electric resistances applied on the spot andcovered by thermic insulating material, like a wrap. The rod to weld, orthe deposit material, has been identified as being the more adequate forthe base metal, taking into consideration the strength it must give tothe base metal.

Besides the incidence of induced distortion in the repaired machine ormachine component, it was also observed that the processes adopted up tonow always accuse failures, mainly failures due to ruptures, in therepaired spot as well as in the rest, more commonly produced by effectsof structural stresses induced by mechanisms of mechanic restriction,due to distortion or even residual stresses developed in elements ofhigh variation of section modules, or inadequate deposit. These effectshave greatly prejudiced such repairs.

SUMMARY OF THE INVENTION

The present invention relates to an integrated process for repair inwhich a rod or deposit material is selected or elaborated after a basematerial has been accurately analyzed.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In this invention, called integrated process to repair, the rod ordeposit metal is selected or elaborated after the base metal isaccurately analyzed, provided that the deposit metal is not a strangeelement. These analyses identify, in addition to the chemicalcomposition and the metallurgic condition, the physical condition andthe process to obtain said base metal.

Still according to the process of this patent, after the chemical and/ormechanical cleaning of the surface of the element to be repaired, allthe existing difficulties appear clearly, besides the one alreadydetected which characterized the failure, by means of non-destructivetests and sampling.

Once all the existing difficulties are identified, the squashed orsmashed zones are superficially removed and the cracks and fissure areopened with chamfers produced by mechanic means or carbon. The remotionprocesses and the opening are executed without any residual stress atsignificant levels, and with the use of pre-heating and/or superficialmechanic remotion after the operations perfomed with heat.

Once the remotion and the opening to be repaired are performed andcleaned, points of reference are determined for the dimensional controlduring the welding process, in order to preserve the dimensionalcondition of the element. These points of reference are determinedaccording to the characteristics of the biggest opening to be repairedand to the main axles of the element. The points of reference arecreated by the welding, in the element, of pins in the extremities ofthe reference measures.

Depending on the dimensions of the element and on the repairs to beperformed, this element is hypothetically divided in zones with similarmasses as symmetrically as possible. A center of mass is determined foreach zone, as accurately as possible, where the applications ofthermocouple will be made for the effective control over the temperaturevariations between the different zones. Some mass can be added tocontrol the temperature between these zones, in order to minimize thethermic inertia between each zone.

Once the remotions, the opening to be repaired cavities, the referencepoints for the dimensional control and the zones of thermic control aredefined, processed and cleaned, the final position of the element isdefined, for the welding. The ideal support is isostatic, but thehyperstatic one can also be used.

Then, the normal electric resistance are distributed on the surfaces tobe heated, to prepare the process of welding, the zones being insulatedby pieces of technical ceramic, with quick clamp terminals in theextremities for coupling with cables of high amperage. The amount ofelectric resistance to be applied on the surface of each zone depends onits thermic inertia.

After the application of the electric resistances, the element isthermically insulated in 25 mm layers of ceramic fiber wraps, for anideal insulating of 10 C.°/mm for a typical temperature of stressrelief. Once the element is insulated, leaving open windows when thereare opening to be repaired, it is belted in order to fix the insulatingsystem. The pins for the points of reference must show up in theinsulating layer.

The next step is to heat the element up to a temperature of 300 C°. Themaximum heating rate in all zones must be 150 C.°/h.

Before starting the welding operation, it is necessary to make a heattreatment to relief the stresses the element acquired during itsoperational lifetime, making sure it is free from prewelding stressesand assuring it has the original properties of strength, resiliency andcontinuity. The thermic welding level must be the highest possible one,merely conditioned to the hardness the base metal must keep, dependingon its physicmetallurgic structure. This level is, at least, the minimumtemperature of stress relief for said base metal.

During the welding operation, the dimensional state of the element iscontrolled by means of reference pins, monitored by micrometric screws,comparative gauge or similars, and with the thermic control of the zonesby compatible thermocouples and pyrometric system.

All the welding operations follow this sequence: opening of theinsulating through the corresponding window, welding, cleaning, closingof the window, thermic equilibrium and dimensional conference. Thisprocedure is repeated as many times as necessary until the welding isperformed within the specified dimensions.

Once the welding is finished, the temperature level must be maintainedlong enough in order to relieve the welding stresses.

The cooling rate of each zone at the end of the relief phase iscontrolled, its cooling speed being the result of its thermic inertia.

When the element is cooled and attains the temperature of 80 C.°, aseries of non-destructive tests are performed on the repaired zones.With the element at a metrological environmental temperature, itsdimensions are confirmed, and the programme of machining "in loco" orwith machines is established, for the zones with additional over-metal.

The process dealt with in this patent allows excellent results ofmachining "in loco" as well as with machines, and is characterized asbeing quick, efficient and of low cost when compared to the replacementof the element.

With this process, the element is restored with the same characteristicsit had when new.

I claim:
 1. A mechanical-metallurgic process for repairing machinecomponents damaged by cracks, fissures, wearings or dents, made ofmetallic material, the steps comprising:initially cleaning chemically ormechanically a surface of a component to be repaired revealing allexisting difficulties; non-destructive testing and sampling definingdifficulties and analyzing characteristics of the components basematerial; selecting a welding rod or addition material that isappropriate to the base material; superficially removing surface damagezones, and providing cracks or fissures with chamfers producedmechanically or by carbon are defining reference points for adimensional control during a welding process, for dimensionallymonitoring said component, said reference points are determinedaccording to characteristics of a biggest opening to be repaired andmain axles of the component, said reference points being created bywelding, in the component, of pins in extremities of reference measures;hypothetically dividing the component into zones with similar masses, assymmetrically as possible, wherein for each zone, a center of mass isdetermined as accurately as possible; applying thermocouples in thecenter of each zone for effective control of temperature variationduring the whole process; final isostatic positioning of the elementpreferentially, or, as a second option, hyperstestic positioning ofwherein the element; applying normal electric resistance for heating forthe welding process on zones to be heated, wherein the resistance amountis distributed on the surface of each zone depending on its thermicinertia, the electric resistance being insulated with pieces of ceramic;applying thermic insulating covering the area of repair difficulties,belting the insulation for fixation, the pins for the reference pointsbeing long enough to show up in the insulating layer; applying heat upto a temperature of 300 C.°, wherein the heating rate in all the zonedoes not exceed 150 C.°/h; applying heat treatment for stress reliefthereby eliminating or minimizing pre-welding stresses; applying weldingthrough said windows to an area to be repaired; dimensionallycontrolling the component by said reference pins, monitored by a systemof micrometric screws, or comparative gauges, and the thermicallycontrolling the zones by compatible thermocouples and pyrometricsystems, wherein when the component is highly complex, with many pointsfor a dimensional and/or thermic control, a computerized control systemis used; said welding being in the following sequence: opening of theinsulation by a corresponding window, welding, cleaning, closing of thewindow, thermic equilibrium and dimensional conference, repeating thisprocedure as many times as necessary until the welding is performedwithin the specified dimensions; after the welding is finished,maintaining the temperature level long enough to relieve the weldingstresses, and cooling at a controlled rate to a temperature of 80 C.°;and at an environmental temperature, performing dimensional tests andnon-destructive tests, and repeating the above process if necessary.